Species Agave sisalana, or sisal, as it is commonly called, is a plant of Agavaceaw family. Its fiber has been recognized as the most important of the leaf fiber group. This group consists of hard, coarse fibers. Such fibers, often referred to as “hard fibers”, are usually long and stiff and are typically used in the cordage industry to produce ropes and twines. Other than its agricultural uses, sisal is also employed by the marine, shipping and industrial sectors to produce rugs, matting, brushes and marine-type ropes. Sisal pulp is also used in paper industry. Sisal pulp has certain characteristics such as high tear resistance, high alpha cellulose content, high porosity, high bulk, high absorbency which make sisal pulp suitable for many specialty papers.
Long sisal fiber and its products is the mainstay of the industry and this is what has kept the industry going. This is, however, only two percent of the sisal plant. The rest is a biomass and short fibers which have been thrown away or burn at cost financially and environmentally. In the worldwide production of fiber of 300,000 tons, about 15,000,000 million tons is the biomass and short fibers called “waste”. This is more prevalent in Africa where the mode of production has predominantly been estate based and therefore leaves are transported to a central factory for decortication thus disposal of this huge amount of biomass becomes a problem. The traditional answer has been to pump in a lot of water to convey this material from the decorticator, at some places directly into a river causing oxygen depletion in the water. The return from the plant therefore has been low due to this low utilization.
Research has been going on to establish how best to exploit this huge quantity of biomass commercially. Focus is now on using this as a source of energy (biogas and electricity), animal feed, organic soil improver, pharmaceuticals, and raw materials for bags and padding.
Furthermore, the sisal industry is concentrated in the mostly tropical regions of Africa, Central and South America and Asia (particularly China). It is produced in some of the poorest areas of the world and in many cases it is the only source of income and economic activity in those areas. Thus it contributes significantly to the efforts to reduce poverty and provide rural employment to nearly six million people.
Therefore, it is beneficial if short sisal fiber can be utilized in the construction industry where bulk volume of raw material consumption is commonly required.
U.S. Pat. No. 6,017,595 (to Brenot et al) discloses a mixed composition for making structural building materials, which comprises a reprocessed waste material such as impure lime obtained from water treatment plant; a reinforcing material such as fiberglass, metal material, sisal fiber, or plastics; and a polymeric material preferably including polyurethane foam. More specifically, Brenot et al teach the mixed composition comprising 20 to 40% of waste material, 5 to 20% of reinforcing material, and 40 to 75% of polymeric material. U.S. Pat. No. 6,438,915 (to Beauboeuf) discloses a prefabricated wall panel as a new type of wall structure. The wall panel is composed of perlite, cement, water and sisal fibers of 1 to 2 inches length.
On the other hand, light weight concrete has been produced with various compositions for construction industry. Perlite is a common component of light weight concrete. Perlite is a generic term for naturally occurring siliceous rock. There are many uses for perlite, generally in three categories, construction applications, horticultural applications and industrial applications. Because of perlite's outstanding insulating characteristics and light weight, it is widely used as a loose-fill insulation in masonry construction. In addition to providing thermal insulation, perlite enhances fire ratings, reduces noise transmission and it is rot, vermin and termite resistant. When perlite is used as an aggregate in concrete, a light weight, fire resistant, insulating concrete is produced that is ideal for roof decks and other applications. Perlite can also be used as an aggregate in Portland cement and gypsum plasters for exterior applications and for the fire protection of beams and columns. Other construction applications include under-floor insulation, chimney linings, paint texturing, gypsum boards, ceiling tiles, and roof insulation boards.
Most of light weight concrete is used for building and roof constructions, which possess many basic properties of regular concrete, such as strength and hardness. These materials can not be machined, nailed or screwed like wood materials. Therefore, their utilities are limited to only certain applications.
In another aspect, air-entraining agents are commonly used in producing Portland and masonry cement, and other construction materials. Air entrainment is the process whereby many small air bubbles are incorporated into concrete and become part of the matrix that binds the aggregate together in the hardened concrete. These air bubbles are dispersed throughout the hardened cement paste; they act like flexible ball bearings increasing the plasticity and workability of the cement paste. Entrainment of air is accomplished by the development of microscopic bubbles, introduced by agitation and stabilized by the air-entraining agents in the paste phase of the mortar or concrete. It is known that the use of air-entraining agents increases freeze-thaw and scaling resistances of the air-entrained concrete, improves placeability, and reduces bleeding and segregation of fresh concrete. The air-entrained concrete is more workable than non-entrained concrete.
The air-entraining agents are organic additives, and most commonly used are chemical surfactants which can be categorized into four groups: salts of wood resins; synthetic detergents; salts of petroleum acids; and fatty and resinous acids and their salts. One of commonly used air-entraining agents in cement industry is an aqueous solution of neutralized hydroaromatic and fatty carboxylic acids, commercially available under the trade name of Airalon®, from Grace Construction Products, Cambridge, Mass. 02140. It is known that Airalon® generates stable air, has low addition rates, and it is easy and safe to handle. The dosage rate of Airalon® depends on the fineness and the air content requirement of each cement, and it is in general in a range from 0.03% to 0.35%.
German patent No. 00203549 A3 discloses a machinable, nailable, and screwable wood-based concrete. The concrete consists of Portland cement, concrete sand, and wood chips in a volume ratio of 1:1:4. To produce this concrete, coarse wood chips is soaked in water for 48 hrs, then mixed with cement and concrete sand to form the wood concrete. Although the prior art expands the concrete properties, it is evident from the composition that a large quantity of wood is required for making such a concrete. It is known to the general public that wood is one of the most valuable natural resource and preservation of trees and forests has significant impacts on our environment.
Based on the above described, it is apparent there is need for an improved light weight concrete which does not use wood, but possesses wood properties so that the concrete can be machined, nailed, and screwed. There is also a strong need for effectively utilizing short sisal fibers in construction or other industries, to turn the current waste into valuable raw material source.